Very basic RAM question 133 vs 2700

[nickbirkby]

Hello all,
This afternoon I have been trying to max out my MDD 2003 1.25 with 1.5gig of RAM. I have been going through what Ram I have in different machines and discovered that its almost all PC133 and not the PC2700 that is supposed to be the optimal for this machine.

So I now have one stick of 512m 2700 ram and the rest is PC133 making up 1.5gig. Works fine so far.

My question is this: is the difference in performance very significant between the two? I am keen to use the correct spec of course.

Sorry its a rather basic question, but I'm not that clued up on this and am now curious. Thanks so much.

[robespierre]

The numbers aren't measuring the same thing. PC133 means 133 MHz. PC2700 means 2700 MB/s (in fact it's only 2666.66).
The latter has a higher clock speed (166.66 MHz) but more importantly it is Double Data Rate, so it transfers twice per clock cycle.
So yes, there is a large difference in potential performance, but I can't say whether that will matter on the MDD.

[GaryN]

So I now have one stick of 512m 2700 ram and the rest is PC133 making up 1.5gig. Works fine so far.

I'm puzzled. AFAIK, PC133 RAM is typically a 168-pin SIMM while the PC-2100 or PC-2700 found in the MDD are 184-pin.
So I'm not sure how you can have the PC-133 installed and working…?

The PC-133 was common in the Quicksilvers with their 133MHz data bus.
The MDD's have either a 133MHz bus in the 867MHz and 1.0GHz machines or a 167MHz bus in the faster ones.
So, your (either) single or dual 1.25MHz machine wants PC-2700.
   * You can also use PC-3200. It will work fine though it will run at PC-2700 speed.
The optimum config for the MDD is four 512Mb PC-2700 SIMMS.

[Protools5LEGuy]

I am in front of my MDD 867 dual and Apple System Profiler says

DIMM 0 PC 2600U-30330

DIMM 2 PC133 CL3

DIMM 3 PC133 CL3

All 512 DDR AFAIK

[nickbirkby]

Thank you for the replies. Its a bit confusing but I get the idea. To be clear the machine is a single processor 1.25 built 2003 and it shipped with PC2700

Im assuming the machine has a 167mhz bus, so I am 37 mhz under spec.

GaryN the 133 ram appears physically identical to the 2700 as far fitting the slots goes.

The PC2700 ram seems a little scarce/ expensive - at least where I live, but I can add 3200 to my options then.

Last rather newb question, if Im changing ram around in machines is there any wisdom in doing a p-ram reset on startup with a new config of ram? (conltrol-alt-p-r) Or is that just for if there is a problem with booting?

Thanks again.

[refinery]

it could just be a case of some poor choices in labeling. PC133 typically refers 133mhz SDR memory, but if you wanted to be semantic about it, DDR-266 technically is still 133mhz ram, it just processes data at double the rate, hence 266.
not unusual for something like that to happen when a new standard comes out and not everyone is adhering to it fully yet.

[GaryN]

I am in front of my MDD 867 dual and Apple System Profiler says DIMM 0 PC 2600U-30330

On the MDD, ASP has a bug that reports PC2700 RAM as PC2600, which doesn't exist.
PC133 is the clock speed which is correct for a 867MHz MDD

So I now have one stick of 512m 2700 ram and the rest is PC133 making up 1.5gig. Works fine so far.

So, nickbirkby… I see you have now added:
"GaryN the 133 ram appears physically identical to the 2700 as far fitting the slots goes."
Thank you for that. I was really scratching my head because you went back and edited out the original statement about pin count on those SIMMS. 

It's no necessary to reset the PRAM after changing the memory sticks. The system will recognize it by itself.

[nickbirkby]

Thanks GaryN for clearing up the Pram reset question.
Btw, I didnt actually mention the simm pin count on the original post, I forgot.

Im now going to try and cobble together a mix of 3200 and 2700 and see how it goes.

Thanks to all for the replies, much appreciated